The present invention relates to a method of production of a pressure sensitive adhesive sheet capable of preventing or removing trapped air, or a blister.
When manually sticking a pressure sensitive adhesive sheet on an adherend, there has been a problem that an air trapping can be formed between the adherend and the adhesive face so that the pressure sensitive adhesive sheet is disfigured in some cases. This air trapping is likely to occur more often when the area of the pressure sensitive adhesive sheet is large.
In order to solve the problem in the appearance of the pressure sensitive adhesive sheet due to the air trapping, it has been performed that a pressure sensitive adhesive sheet is replaced by the other pressure sensitive adhesive sheet, a pressure sensitive adhesive sheet is removed and attached again, or a hole is formed using a needle in the expanded portion of the pressure sensitive adhesive sheet to deflate air in question. However, the following problems have often occurred. For example, when replacing the pressure sensitive adhesive sheet, it is not only troublesome, but also causes an increase in the cost. In addition, when attaching the pressure sensitive adhesive sheet again, the pressure sensitive adhesive sheet may be damaged, wrinkles may be generated on the surface, or the pressure sensitive adhesive properties may be deteriorated. On the other hand, the method to make a hole using a needle disfigures the pressure sensitive adhesive sheet.
In order to prevent an air trapping, there has been used a method to attach water onto the adherend or the adhesive face in advance of sticking. However, when large-size pressure sensitive adhesive sheets such as a glass shatterproof film for windows, a decorative film, a marking film or the like are stuck, much time and much effort are required. In addition, apparatus have been used to stick such sheets to prevent an air trapping rather than manual work. However, sticking by apparatus cannot always be applied depending on uses of the pressure sensitive adhesive sheet or portion and/or shape of the adherend.
In the meantime, resin materials such as an acrylic resin, an ABS resin, a polystyrene resin, a polycarbonate resin or the like generate gas either by heating or without heating. When a pressure sensitive adhesive sheet is stuck to the adherend made from such a resin material, the gas generated from the adherend causes a blister in the pressure sensitive adhesive sheet.
In order to solve the above problems, there has been proposed a pressure sensitive adhesive sheet where a plurality of independent small projections are placed in a disseminated dot state on an adhesive face of the pressure sensitive adhesive layer in Gazette of Japanese Utility Model Registration No. 2503717 and Gazette of Japanese Utility Model Registration No. 2587198. In this pressure sensitive adhesive sheet, the tip of the small projections of the pressure sensitive adhesive layer is closely contacted to the adherend and the flat base surface of the pressure sensitive adhesive layer is kept spacing from the adherend, therefore a gap leading to the outside between the flat base surface of the pressure sensitive adhesive layer and the adherend is formed. Consequently, by deflating air or gas from the gap to the outside, an air trapping or a blister can be prevented.
However, on the pressure sensitive adhesive sheet disclosed in the above gazettes, there have been problems that an adhesive strength is poor because only the tip of the small projections in the pressure sensitive adhesive layer is bonded to the adherend, and water, chemicals or the like can easily be infiltrated between the pressure sensitive adhesive layer and the adherend, thus lowering an adhesive strength moreover. Even though such an adhesive sheet is strongly pressed to the adherend, an adhesive strength is not strong enough due to the small projections of the pressure sensitive adhesive layer. Furthermore, in that cases, the gap leading to the outside is filled up, therefore a blister cannot be prevented, which is formed while gas is generated from the adherend.